Thermal relay



1961 c. K. STROBEL ETAL 3,003,086

THERMAL RELAY Filed June 19, 1958 CharlesKStrobel,

United States Patent g This invention relates to heat motor electric relays and more particularly to thermally operated bimetallic relays.

It is an object of this invention to construct a heat motor relay which can be'used in both A.C. and DC. electric circuits. A

Another; object of this invention is to reduce the possibility of sticking contacts and insure fast contact operation in a heat motor relay of the indicated type.

Another object of this invention is to design a heat motor relay of the indicated type which will compensate for changes in supply voltage.

Anotherobject of this invention is to insure accurate ambient. temperature compensation in a heat motor relay of the indicated type.

In a preferred embodiment of the invention, the electric relay includes a pair of relay contacts mounted in opposed relation on a pair of bimetallic strips mounted in parallelrelation for cantilever movement. The relay contactsare adapted to beelectrically connected in the electric circuit to be controlledby the electric relay. The bimetallic strips are constructed and arranged to move in the same sense in response to an increase or decrease in the temperature thereof. 7 A control circuit is provided for controlling the movement of one of the bimetals toward and away from the other of the bimetals to open and close the relay contacts. This control circuit includes an ON-OFF switch and an electric heater positioned in proximity with the controlled bimetal. When the switch is closed, the heater is operative to heat the controlled bimetal and when the switch is open, the heater is inoperative. A short circuit means is connected in parallel with the electric heater for discontinuing the contact closing movement of the controlled bimetal by short circuiting the electric heater. This short circuit means is arranged to short circuit the electric heater only after the relay contacts have been closed force.

The above and other objects and features of the invention will appear more fully hereinafter from a considera-. tion of the following disclosure taken in connection with the accompanying drawings wherein:

FIG. 1 is a perspective view of a preferred embodiment of the invention;

FIG. 2 is a schematic showing of the embodiment shown in FIG. 1; and

FIG. 3 is a schematic showing of a modified form of the invention.

Referring now to FIGS. 1 and 2, the heat motor relay illustrated therein is adapted for single-pole, single-throw normally 'open relay contact operation. A bimetallic strip is secured at one end in cantilever fashion on the lower portion 12 of a two-piece mounting post 14 by means of screws16 A relay contact 18 is mounted on the free end of bimetallic strip 10 by means of an insulating support member 20 riveted or otherwise secured to bimetallic strip 10. A second bimetallic strip 22 is with a predetermined contact Patented 'Oct. 3, 1961 v with reference to bimetallic strip 10. A second relay contact 28 is mounted on the free end of bimetallic strip 22 by means of an insulating support member 30 riveted or otherwise secured to bimetallic strip 22 and is positioned in opposed relation to relay contact 18. The upper portion 24 of two-piece mounting post 14 can be rotated l with respect to lower portion 12 to adjust the spacing of I 3 be apparent that when therelay contacts 18 and 28 are secured'at one endiacantilever fashion on theupper mounting post 14 by means of it is to the opposite side of mounting post 14 relay contacts 18 and 28. Bimetallic strips 10 and 22 are constructed so as to deflect in the same direction upon an increase .in the temperature thereof. Bimetallic strip 22 is so positioned that, upon an increase in the tempera ture thereof, it is deflectable toward'bimetallic strip 10 to therebyclose relay contacts 18 and 28. by

Relay contact 18 is electrically connected to-a terminal 32 by means of a connector 34 and relay contact 28 is electrically connected to a terminal 36 by means of a connector 38. Terminals 32 and 36 are in turn connected to the electric circuit to be controlled by the electric relay. This circuit maytake the form of an electric heating means 40 connected to a source of electrical energy'SI through relay contacts 18., and 28. It will closed, electric heating means 40 is supplied with electrical energy from source S1 and when relay contacts 18 and 28 are open, no electrical energy is supplied to electric heating means 40.

A control circuit is provided for opening and closing relay contacts 18 and 28. This circuit includes an electric heating coil 42 which is wound around bimetallic strip 22 for heating the same andiselectrically insulated therefrom by suitable insulating tape 44 wrapped around bimetallic strip 22. One end of heater coil 42 is con nected to a terminal 46 mounted on mounting post .14 and the other end of heating coil ,42 is connected to the freely. movable endof bimetallic strip. 22. Terminal 46 is electrically connected to a terminal 50 by connec tor 52 and the fixed end 'of bimetallic strip 22 is elecf trically connected to a terminal 54 by a connector 56. It will be apparent that the heating current passes from terminal 50,.through connector 52, heating coil 42, bimetallic strip 22 and connector 56 to terminal 54.

Control circuit terminals 50 and 54 are connected to a source of electric energy S2 by means of connectors 58 and 60, respectively. A switch 62 is serially connected in connector for controlling the "flow of electrical energy from source S2 to electric heating means 42. Switch 62 may be adapted to be operable between an open position wherein electric heater-42 is not connected to source S2 and a closed? position in which heating means 42 is connected to source S2. The operating mechanism for switch 62 may take the form of a thermostatic means (not shown) responsive to the temperature of the space surrounding heating means 40. V

It will be apparent that when the heating circuit is closed by switch 62; the heat applied to bimetallic strip 22 will raise the temperature thereof and cause deflection toward bimetallic strip 10. As long as switch 62 is closed,

,bimetallic strip 22 will continue to deflect toward biwith bimetallic strip 22 during the opening of these con tacts. However, this does not insure fastoontact opening. Thus, means are provided for maintaining a stable contact closing force between relay contacts 18 and 28. Such means takes the form of a short circuit'connection 64 for discontinuing the operation of the heating tztgil 42 upon a predetermined deflection of bimetallic strip Short circuit connection 64 includes an electrical connector 66 connected between terminal 46 and a control contact 68 which is threadedly mounted on the free end of a cantilever bimetallic strip 70 having a fixed end thereof secured to a mounting post 72. A second control contact 74 is mounted on the free end of bimetallic strip 22 in opposed relation to control contact 68. Control contacts 68 and 74 are normally spaced part by a distance greater than the normal spacing of relay contacts 18 and 28. It will be apparent that the spacing of control contacts 68 and 74 is adjustable by rotation of control contact 68. The short circuit currentpasses from terminal 46 through connector 66, control contact 68, and control contact 74 to the free end of bimetallic strip 22 to thereby short circuit the heating coil 42.

In the operation of the single-pole, single-throw embodiment of the invention, the normally open position is illustrated schematically in FIG. 2. In this position, switch 62, relay contacts 18 and 28, and control contacts .68 and 74 are all open. When switch 62 is closed, the. heating current passes through heating coil 42 which heats bimetallic strip 22. As the temperature of the bimetallic strip increases, it deflects toward bimetallic strip thereby moving relay contact 28 toward relay contact 18 and control contact 74 toward control contact 68. As the relay contact spacing is less than the control contact spacing, relay contacts 18 and 28 will come into engagement first. As bimetallic strip 22 continues to deflect, bimetallic strip 10 will deflect therewith and the relay contact closing force will be increased until control contacts 68 and 74 come into engagement to complete short circuit connection 64. At this point, the electrical energy from source S2 will be short circuited through short circuit connection 64 and relatively little current will pass through the heating coil 42. Hence, heating coil 42 will cease producing heat and the temperature of bimetallic strip 22 will decrease with the result that, after a short override movement toward bimetallic strip 10 we point of maximum deflection, bimetallic strip 22 will deflect away from bimetallic strip 10 thereby decreasing the relay contact closing force. It will thus be apparent that the amount of deflection of bimetallic strip 22 toward bimetallic strip 10, and hence the maximum relay contact closing force, is dependent upon spacing between control contacts 68 and 74.

As bimetallic strip 22 returns from the point of maximum deflection, the relay contact closing force decreases until control contacts 68 and 74 become separated, at which point the electrical energy from source S2 will cause a current to pass through heating coil 42. Heating coil 42 will in turn heat bimetallic strip 22 to increase the temperature thereof and, after a short return override movement, bimetallic strip 22 will again deflect toward bimetallic strip 10.

It will be apparent that the electric relay will recycle as described above as long as switch 62 remains closed. The initial relay contact and control contact spacings are adjusted so that relay contacts 18 and 28 remain closed at all times during the recycling operation whereby electric heating means 40 will receive a steady supply of electrical energy from source S1. However, upon a subsequent opening of switch 62, the electric relay will return to the normally open position shown in FIG. 2 in which relay contacts 18 and 28 are open thereby disconnecting the supply of electrical energy to electric heating means 40 from source S1.

In order to insure electric relay operation which is unaffected by ambient temperature variations, bimetallic strips 10, 22 and 70 are constructed and arranged sothat the contact carrying ends will move the same amount and in the same direction upon ambient temperature variations. Similar compensation may be obtained by making bimetalilc strip 70 of the same dimensions as bimetallic strips 10 and 22 and mounting bimetallic. strip 70 on mounting post 14.

Since bimetallic strips 10 and 22 are mounted on opposite sides of mounting post 14, the free ends thereof will deflect about spaced axes. Hence, the relay contacts 18 and 28 open with a shearing movement which will reduce the possibility of sticking contacts. When large control currents are used, stop 63 will further reduce the possibility of sticking of thecontacts.

For optimum operation, the heating current and the relay contact spacing are chosen so that relay contacts 18 and 28 close a few seconds after switch 62 is closed. The spacing between control contacts 68 and 74 is adjusted so that the heating coil 42 is short circuited after relay contacts 18 and 28 are closed so as to provide a stable relay contact closing force and maintain the relay contact opening time a few seconds after switch 62 is opened. The intermittent short circuiting of heating coil 42 by the control contact operation, permits the use of a high heating rate for quicklyclosing relay contacts 18 and 28 with provision being made for maintaining a stable contact closing force and quiet opening. It will thus be apparent that the control circuit voltage changes at electrical source S2 will have little effect on the timing when the heating rates are high enough for contact closing movement within a few seconds.

The embodiment of the invention shown in FIG. 3, wherein parts corresponding to parts hereinbefore described are given like reference numerals, is similar in construction and operation to the embodiment shown in FIGS. 1 and 2 and diflers therefrom only in the addition of another relay for single-pole, double-throw operation. In this embodiment, relay contact 28 is formed with a back contact portion 76 extending from the opposite side of bimetallic strip 22 to that side firom which relay contact 28 extends. A third relay contact 78 is mounted in opposed relation to back contact portion '76 on the free end of a bimetallic strip 80 secured at one end in cantilever fashion on a mounting post 82. Bimetal strip 80 is normally positioned parallel to bimetal strip 22 and is constructed to deflect in the same sense by the same amount as bimetal strips 10 and 22 in response to ambient temperature variations. Relay contacts 78 and 28 are serially connected in a second electric circuit to be controlled by the electric relay. This circuit may take the form of an electric heating means 84 connected to a source S1 through relay contacts 78 and 28.

The single-pole, double-throw electric relay is normally positioned as shown in FIG. 3 with relay contacts 28 and 78 electrically connected because of the engagement ofrelay contact 78 with back contact portion 76 of relay contact 28. This completes the circuit from source S1 through heating means 84. When switch 62 is closed, bimetallic strip 22 will deflect in the manner hereinbefore described to control the activation of electric heating means 40 and open relay contacts 28 and 78 to discontinue the flow of electric energy from source S1 to electric heating means 84. A stop 86 is positioned between bimetallic strips 22 and 80 to limit the movement of bimetallic strip 80 along with bimetallic strip 22 should relay contact 78 stick to back contact 76. When the switch 62 is subsequently opened, the parts will return to the position shown in FIG. 3, thereby closing the circuit to electric heating means 84 and opening the circuit to heating means 40.

The heat motor electric relay shown and described has certain advantages over the magnetic relay. The heat motor electric relay can be used interchangeably in A.C. or DC. circuits and in circuits having a sensitive switching device which might fluctuate during certain periods of its operation and operates without contact chatter at all times.

It is to be understood that although several embodiments of this invention have been shown and described, the invention can be variously embodied and changes may be madein the constructionand arrangement of parts 1. In an electric relay, the combination a pair of relay contacts for controlling a loadcircuina first heat responsive bimetallic strip supported, atone end for deflection thereabout and having one of said contacts dielectrically mounted on themovable portion thereof, a second heat, responsive bimetallic strip supported at one end for deflection thereabout and having the other of said contacts dielectrically mounted on the movable portion thereof in opposed relation to said one of'said contacts, said first and second bimetallic strips having a normally open position in which said relay contacts are normally spaced apart, said first bimetallic strip. being responsive to an increase in the heat applied thereto to deflect toward said second bimetallic strip and responsive to a decrease in the heat applied thereto to deflect away from said second bimetallic strip, engagement of said first and second relay contacts deflecting said second bimetallic element an amount in proportion to the force of engagement, first circuit means for controlling the deflection ofsaid first bimetallic strip toward said second bimetallic strip, said first circuit means including an electric heater, a first switch means operable between a first control position for connecting said heater to a source of electric energy and a second control position for disconnecting said electric heater to said source of electric energy, said electric heater being positioned in proximity with said first bimetallic strip for heating the same when said first switch means is in said first control position to cause movement of said first bimetallic strip toward said second bimetallic strip, and second circuit meansfor discontinuing the operation of said first circuit means to cause deflection of said first bimetallic strip toward said second bimetallic strip, said second circuit means including a short circuit connection electrically connected in parallel with said electric heater, a second switch means serially connected in said short circuit connection and operable between a circuit making position in which said short circuit connection discontinues the operation of said electric heater and a circuit breaking position in which said short circuit connection permits the operation of said electric heater, said second switch means including a first control contact mounted on the outer end of said first bimetallic strip for movement with said first bimetallic strip and a second control contact adjustably positioned in opposed relation to said first control contact for making and breaking contact therewith upon movement of said first bimetallic strip toward said second bimetallic strip, said second control contact being positioned so that the distance said first bimetallic strip must deflect from said normal position to close said control contacts is greater than the distance that said first bimetallic strip must deflect firom said normal position to close said relay contacts, whereby the engagement pressure of said relay contacts is substantially constant so that deenergization of the first circuit means results in rapid disengagement of said relay contacts.

2. Adevice as claimed in claim 1 wherein said one end of said first bimetallic strip is movable to adjust the position of said one of said relay contacts and said second control contact is adjustable to vary the spacing of said control contacts, to vary the engagement pressure of said relay contacts mounted on said bimetallic strips. 7,

3. In an electric relay, the combination comprising a first heat responsive bimetallic strip mounted for cantilever movement about an axis, a second heat responsive bimetallic strip mounted for cantilever movement about an axis and positioned in parallel relation with said first bimetallic strip, a third bimetallic strip mounted for cantilever movement about an axis and positioned between said first and second bimetallic strips in parallel relation thereto, a first relay contact dielectrically mounted on the movable portion of said first bimetallic strip, a second relaycontact dielectrically mounted on the movable portion oisaid second bimetallic strip, a third relay contact dielectrically mounted on the movable portion of said third bimetallic strip in opposed relation to said first and second relay contacts for engagement therewith, said first and third relay contacts being adaptable for controllinga first electric. circuit, said second and third relay contacts being adaptable for controlling a second electrical circuit, saidbimetallic strips being normally posi-o tioned with said second and third relay contacts in engagement with said first and third relay contacts spaced apart, and said bimetallic strips being constructed for, deflection in the samesense upon anincrease in the tem+ bimetallic strip for heating the same and a short circuit connection electrically connected in parallel with said electric heater, said short circuit connection having a switch means for closing the same upon a predetermined deflection of said third bimetallic strip, said switch means including a first control contact mounted on the outer end of said third metallic strip for movement with said third bimetallic strip and a secondcontrol contactadjustably positioned in opposed relation to'said first control contact for a switch closing engagement therewith upon deflection of said third bimetallic strip by an amount in excess of said deflection required to close said relay con-r tacts, whereby electric heater is short circuited out of said circuit means so as to maintain substantially constant pressure engagement betwecnvsaid first and third relay contacts. o

' 4. Ane'lectric relay as claimed in claim 3 including a fourth heat responsive bimetallic strip supported at one end for deflection thereabout and having said second control contact mounted on the movable portion thereof.

5. In an electric relay, the combination comprising a pair of relay contacts, a first heat responsive elongated flexible bimetallic strip supported on one end for deflection thereabout, one of said pair of contacts dielectrically mounted on said first bimetallic strip and at the remote pair of contactsindividually connected to said conductors so as to be serially electrically located in their closed positions when said first bimetallic strip is deflected in response to an application of heat thereto to move said one contact towards said second contact to close said pair of contacts, said first bimetallic strip and said first contact displacing said second bimetallic strip and said second contact, a control circuit, a control circuit contact mounted on the remote end of'said first bimetallic strip and being laterally offset relative to the longitudinal length thereof and electrically connected thereto, a second adjustably mounted control circuit contact oppositely disposed from said first control circuit contact, an electric heating means to heat and deflect said first bimetallic stripinto engagementwith said second bimetallic strip to cause relay contact engagement when said control circuit is energized, said electric heating means in said control circuit electrically connected in parallel with said control circuit contacts, said-control circuit contacts energized upon further application of heat to said first bimetallic strip by said electric heating means to-short circuit said electric heating means, said first bimetallic strip relaxing to disengage said control circuit contacts and decrease the pressure of engagement of said relay contacts, said electric heating means then being energized to move said control circuit contacts into engagement with said control circuit contacts thereby retaining said relay contacts in engagement at substantially constant pressure so that interruption of the control circuit rapidly disengages said relay contacts by a shearing movement.

6. In an electric relay, the combination comprising a pair of relay contacts, a pair of heat responsive flexible bimetallic strips supported at one end for deflection thereabout, said pair of strips being spaced apart and being adapted to extend substantially parallel to each other, a pair of contacts secured to each of said strips and being positioned substantially in opposed relationship to each other, an electric heating means operatively associated with one of said bimetallic strips and being adapted to cause contact closing movement with the other of said bimetallic strips, said one bimetallic strip being deflected by said heating means to describe an are great enough to displace said other bimetallic strip thereby achieving a force between the relay contacts proportional to the displacement of said other bimetallic strip, said one bimetallic strip having an extended portion, a control contact located at the remote end of said extended portion, and a circuit means energized by said conrol contact after a predetermined deflection of said one bimetallic strip sufficient for engagement of said relay contacts, said circuit means being operative to short-circuit said heating means whereby said heating means is intermittently energized'to retain said relay contacts on said bimetallic strips in engagement at substantially a constant force, which force is determined by the engagement position of said control contact with said circuit means.

7. In an electric relay device, the combination comprising a pair of relay contacts for energizing a load circuit, a first heat responsive bimetallic strip supported at one end for deflection thereabout and having one of said contacts dielect-rieally mounted intermediate the length of said strip and on the movable portion thereof, a second heat responsive bimetallic strip spaced adjacent said first bimetallic strip and being supported at one end for deflection thereabout in the same sense as said first bimetallic strip and havingthe other of said contacts mounted on the movable portion thereof in opposed relation to said one of 'said contacts, an electrically energized heating means operatively associated with said first bimetallic strip and being adapted for deflecting said first bimetallic striptoward said second bimetallic strip in response to electrical energization of said heating means to close said first and second contacts, and a control circuit for energizing said heating means, said control circuit including a short circuit connection electrically connected in parallel with said heating means and having a switch means for closing said short circuit connection upon a predetermined deflection of said first bimetallic strip, said switch means including a first control contact mounted at the outer end of said first bimetallic strip for movement with the movable portion thereof in response to an increase in temperature of said first bimetallic strip by the heating means, and a second control contact positioned in opposed relation to said first control contact for switch closing contact, said second control contact being adapted to energize said short circuit connection after said first and second'contacts close to thereby deenergize the heating means of said first bimetallic strip, said second control contact disengaging from said first control contact upon cooling of said heating means associated with said first bimetallic strip to thereby energize said heating means for deflecting said first bimetallic strip, said first and second contacts thereby being engaged with a substantially constant force existing therebetwecn.

8. An electric relay as claimed in claim 7 including a third heat responsive bimetallic strip supported at one end for deflection thereabout in a manner similar to said first and second bimetallic strips in response to changes in ambient temperatures, said second control contact being displaced an equal distance as said first and second contacts to thereby achieve a substantially constant contact force between said first and second contacts irrespective of the ambient temperature. 7

References Cited in the file of this patent UNITED STATES PATENTS 2,285,677 Myers June 9, 1942 2,329,119 Jacobs Sept. 7, 1943 2,792,533 Richards May 14, 1957 2,842,642 Colombo July 8, 1958 

